Since well before global warming became a heated political
issue, scientists have been trying to determine the rate at which our
planets temperature is increasing. While placing many thermometers around
the world would appear to be the solution, local temperatures can vary widely
across regions and from one year to the next. Instead, researchers have found
they can obtain a measure of average global temperatures by using
satellites to monitor heat-sensitive objects on the ground. Of these objects,
glaciers are among the most reliable indicators of climate change.

Alpine glaciers, like this one near Mt. McKinley, Alaska, change
in response to the local climate. By monitoring the change in size of glaciers around the world, scientists can learn
about global climate change. (Photograph by Klaus J.
Bayr, Keene State College, 1990)

One
method of measuring glaciers is to send researchers onto the ice with
surveying equipment. The Muir Glacier, shown here around 1950, has been studied for
over 200 years. (Photograph from the American Geographic Society Collection
archived at the National Snow and Ice Data Center, University of
Colorado at Boulder)

Despite typical glaciers massive sizes, monitoring them is not always
an easy task. Only specific types of small glaciers are good measures of
climate change. Some glaciers are too large to measure accurately, and others
are simply too unpredictable. Once scientists find a suitable glacier, they
must take satellite images of the ice for a minimum of five years and compare
the results. They then have to look closely at the outside edge of the glacier
(the glaciers terminus). If a large
percentage of the glaciers edge
is receding then the area around the ice is growing warmer, and if a large
percentage is expanding then the area is growing cooler. When enough
measurements from many different parts of the world have been gathered, the
researchers can determine whether the earth is growing warmer or cooler.